Mild decrease in TBX20 promoter activity is a potentially protective factor against congenital heart defects in the Han Chinese population.

Congenital heart defects (CHDs) are among the most common human structural birth defects, and a leading cause of infant death. The worldwide incidence of CHDs is approximately 8% in newborns1. Most patients require surgery, and some infants develop functional cardiac impairments post-surgery that compromises their entire lives. Current studies have found that both environmental and genetic factors contribute to the occurrence of CHDs2,3,4,5. The complicated network of transcription factors plays a crucial role during cardiogenesis6. These factors interconnect upstream signaling molecules with downstream target genes, which influences cardiac cell migration, proliferation and differentiation7. The function of transcription factors can be affected by either conformational changes or dosage. Dosage of transcription factors could be affected by genetic variants in their regulatory regions, which have been reported to associate with CHD risk8,9. One SNP identified in TBX1 promoter enhances TBX1 expression level and is associated with increased risk of ventricular septal defect (VSD)10. Another SNP in Wnt5a 5’untranslated regions (UTR) decreases Wnt5a expression level and is associated with reduced risk of cardiac conotruncal malformations11. Furthermore, SNPs in GATA4 3’UTR were also reported to increase risk of CHDs by microRNA regulation12. In addition to those studies on individual genes, genome-wide association studies also suggest that a large number of non-coding variants contribute to the risk of cardiovascular disease13,14. These results demonstrated that genetic variants in regulatory regions significantly influence gene expression and cardiogenesis. Thus, we hypothesized that functional regulatory variations in vital transcription factor genes could modulate gene expression and CHD susceptibility. TBX20 is an important transcription factor for cardiac development. Tbx20 null mice stop development at E9.0 and die around E10.5, and display outflow tract defects with underdeveloped short heart tubes, a generalized developmental arrest, and lack of chamber differentiation15,16,17. Tbx20 also actively interacts with other vital transcription factors and interacts with the Wnt and Bmp signaling pathways8,18. Indeed TBX20 expression in humans is primarily located in the first heart field (FHF) and the second heart field (SHF) throughout embryonic cardiogenesis, and is involved in valve elongation and remodeling18,19. Tbx20 also has a dosage effect. Takeuchi found that a 95% reduction of Tbx20 results in embryos lacking an outflow tract, whereas mice with a 60% reduction of Tbx20 have less severe heart developmental defects, presenting with impaired outflow tract septation, right ventricular hypoplasia, and defective valve formation16. It’s worth noting that heterozygous Tbx20 knockout mice are viable and do not show any detectable heart defects20,21. However, the effect of TBX20 dosage in human CHDs has not been fully investigated, and genetic variants in the promoter region have rarely been reported. To investigate the effect of TBX20 expression level on CHD risk, we sequenced the TBX20 promoter region in CHD patients/controls. The minor allele of rs10235849 and the haplotype ATC are associated with reduced CHD risk and contribute to attenuated TBX20 transcription in functional analyses. We demonstrated that a mild decrease in TBX20 expression is related to a lower risk of CHD occurrence in a Han Chinese population.